A 35.0-L cylinder contains 387 g O2(g) at 22.5°C. What mass of O2(g) must be released to reduce the pressure in the cylinder to 5.94 atm, assuming the temperature remains constant?

Answer 1

Use PV = nRT and substitute the conditions for the 5.94 atm.
p = 5.94 atm
V = 35.0 L
R = 0.08206
T = 273.15 + 22.5 = ?
Solve for n and convert n to grams.
x grams = n x molar mass O2.

You started with 387g
You want to end up with x grams
The difference is what you must vent

Answer 2

290.8g